This invention relates to a stationary platen type multicolor original reading device as used in a facsimile device or an electronic copying machine, and more particularly to a stationary platen type multicolor reading device in which the original to be read is illuminated in multicolors for instance in red, green and blue, i.e., the three primary colors.
More specifically, the invention relates to a stationary platen type multicolor original reading device for a color facsimile or a color electronic copying machine, in which one image reading element such as a photo-diode array is used, and wherein illuminating light hues are periodically switched to read the image in different hues, so that a plurality of color signals are obtained for one read line.
FIG. 1 is a sectional view outlining a conventional stationary platen type original multicolor reading device for use in a color facsimile.
In FIG. 1, reference numeral 1 designates an original; 2, a transparent platen; 3, a mirror; 4, a focusing (image-forming) lens; 5, a photo-electric reading element; 6, the output terminal of the photo-electric reading element; 14, an output signal amplifier; 15A and 15B, line memories; and 16, an arithmetic circuit.
Further in FIG. 1, reference numeral 21 designates a red fluoroescent lamp for illuminating the original; and 22, a white fluorescent lamp for the same. The fluorescent lamps 21 and 22 are turned on by high frequency signals, in such a manner that when a given lamp is turned on, the other is turned off.
Further in FIG. 1, reference numeral 10 designates a scanner on which the mirror 3, the lens 4, the photo-electric reading element 5, the red fluorescent lamp 21 and the white fluorescent lamp 22 are mounted, the scanner 10 being driven intermittently in the auxiliary scanning direction; and 11, a guide rail for guiding the scanner 10.
When the scanner 10 is set at a given position on the guide rail 11, the illumination position of the original 1, i.e., the main scanning line on the original is determined.
The original 1 at that position is firstly irradiated by the red fluorescent lamp 21. Light reflected from the rear surface (picture surface) of the original 1 is applied to the lens 4 by the mirror 3, so that the optical image of the picture is formed on the photo-electric reading element 5 (such as a photo-diode array).
The photo-electric reading element 5, being driven by a suitable control means (not shown) in synchronization with the turning on of the red fluorescent lamp, reads as an electrical signal a part of the original image corresponding to one main line at the time of illumination with the red lamp. The electrical signal is stored in the line memory 15A.
Then, the red fluorescent lamp 21 is turned off, while the white fluorescent lamp 22 is turned on. Similarly as in the above-described case, the photo-electric reading element reads as an electrical signal the part, corresponding to the same main scanning line, of the image of the original which is illuminated by the white light. This electrical signal is stored in the line memory 15B.
Thereafter, the scanner 10 is moved by as much as one line in the auxiliary scanning direction along the guide rail. Under this condition, the same reading operation is carried out. By repeatedly carrying out the above-described operation, the original is completely read.
The video signals stored in the memories 15A and 15B are supplied to the arithmetic circuit 16, where they are suitably process in a conventional manner and are then output for printing or for transmission to the receiving end, etc.
It is obvious that, when red, blue and green fluorescent lamps are provided for illuminating the original and are turned on the stated order, a natural color image can be read and transmitted.
In the conventional multicolor original illuminating device as described above, the fluorescent lamps are turned on by the high frequency signal and the scanner is moved by one main scanning line intermittently, for instance, every 5 m sec. Therefore the device suffers from the following difficulties:
(1) A fluorescent lamp has no monochromatic spectrum and has a wide emission spectrum. Therefore, the fluorescent lamp is low in color separating capability. Therefore, the reproduced image is low in color purity or color resolution. The spectral range may be decreased by the use of a filter, but the intensity of the illumination is insufficient in this case.
(2) The illuminance distribution characteristic of a bar-shaped fluorescent lamp is such that the emission intensity is high at the middle of the lamp, but lower towards either end thereof. Therefore, in order to uniformly illuminate the surface of the original, the fluorescent lamp must be much longer than the width of the original. Accordingly, the illuminating device is bulky.
A method of correcting the illuminance distribution characteristic using shading means may be taken into account. However, this method is disadvantageous in that the illuminance of the read surface of the original is low as a whole, and the reading sensitivity and speed are reduced.
(3) The scanner is considerably heavy because the fluorescent lamps in the light source, the image forming optical system and the photo-electric reading element are mounted thereon. Therefore, the scanner has large inertia. Accordingly, it is considerably difficult to accurately intermittently move the scanner a predetermined extremely short distance in a short time--i.e. every 5 m sec. This fact is an impediment in producing an increase in the copying speed or facsimile transmission speed and any improvement in the quality of the reproduced image.